The presently disclosed subject matter relates to a brain-machine interface (BMI) system including: an internal device which is to be implanted in the living body; and an external device which is to be placed outside the living body, particularly to the internal device and a method of controlling the internal device.
An internal device acquires brain waves functioning as a signal source to detect the brain activity, and transmits a signal which corresponds to the brain activity, or that which is obtained by processing the signal, to an external device. The external device operates in accordance with the signal received from the internal device. The internal device disclosed in US 2006/0049957 A1 includes a plurality of electrodes which are to be implanted in the living body to detect brain waves.
An internal device such as described above is implanted in the brain of a patient with amyotrophic lateral sclerosis (ALS) or the like, and communication with the patient is supported. In ALS, in the case of strong degeneration of upper motor neurons, however, brain waves gradually diminish. In order to adequately acquire diminished electroencephalogram signals, it is necessary to design the low-noise performance of a group of signal amplification elements which are mounted on the internal device, while anticipating the levels of the diminished electroencephalogram signals. When such a design is employed, however, the size increase of the internal device due to the scale enlargement of an amplification circuit, and heat generation due to the increase of power consumption are inevitable. Therefore, the design is not adequate for an implantable type internal device.